Pre-exposure of cells, tissues or organisms to a sublethal heat shock renders them resistant to subsequent exposure to severe heat treatments that are normally lethal (Parsell, D. A., and Lindquist, S., Annu. Rev. Genet., 27:437–496 (1993)). This phenomenon is known as thermotolerance. The preexposure also causes enhanced expression of a group of proteins referred to as heat shock proteins (hsp).
Pre-exposure to heat renders cells tolerant not only to subsequent exposure to severe heat, but also to certain other stresses, including ischemic type damage. This has been shown not only in experiments involving cultured cells, but also in intact organs such as, for example, the heart (Richard, V., R. et al., Fund. Clin. Pharmacol., 10:409–415 (1996)).